Ultrasound therapy apparatus delivering ultrasound waves having thermal and cavitation effects

ABSTRACT

A method and apparatus for performing therapy using ultrasound. The apparatus uses a treatment device having at least one piezoelectric transducer element to supply ultrasonic waves focussed onto a focal point or region that determines the tissue zone submitted to therapy. The treatment device, which is controlled by a control device, supplies two types of ultrasonic waves, the first one being thermal waves that produce a predominantly thermal effect on the tissue being treated and the second one being cavitation waves that produce a predominantly cavitation effect on the tissue to be treated.

BACKGROUND OF THE INVENTION

The present invention essentially relates to an ultrasound therapyapparatus which delivers ultrasound waves that produce thermal andcavitation effects.

The present invention also relates to therapy apparatus employingultrasound, fitted with a cooling device.

It is known that a high-power focused ultrasound acoustic field is ableto destroy human body tissue (see PCT published applications in the nameof Fry W0-89/07907 and W0-98/07909).

Dunn and Fry have also described in "Ultrasonic threshold dosage for themammalian central nervous system" IEEE transactions, volume BME 18,pages 253-256 how this destruction process involves two effects, morespecifically a thermal effect and a cavitation effect.

The thermal effect predominates when the acoustic power at the point offocus is below a determined threshold of about 150 W/cm² at 1 MHz. Thisthermal effect is due to the acoustic absorption of the tissue, whichconverts the mechanical energy of the acoustic wave into thermal energy.

The cavitation effect becomes predominant when the acoustic power at thepoint of focus exceeds a threshold of 150 W/cm². This cavitation effectis linked to the formation of microscopic bubbles of gas which explodewhen they reach a critical diameter with local release of appreciableamounts of energy leading to destruction of neighbouring tissue.

In order to obtain destruction of tissue exclusively by thermal effects,it is necessary for the acoustic field to be able to reach a thresholdof destruction referred to as the "thermal dose". This threshold is afunction of temperature reached and of the duration of application. Itis thus possible to destroy tissue by application of a moderatetemperature increase over a long duration of application or, on thecontrary, through application of a significant temperature increase overa short period of application.

The temperature increase is directly linked to the acoustic power of theultrasound field at the point of focus.

In the case of a moderate temperature and a long duration ofapplication, transfer and spreading of heat energy occurs around thepoint of focus, notably due to thermal conduction in the medium and toblood flow, which leads to poor control of the volume being treated,which may lead to healthy zones being destroyed with a resultantimpairment of the quality of treatment.

In the case of elevated temperature and a short duration of application,the acoustic power at the focal point exceeds the abovesaid cavitationthreshold, with the resultant obtaining of cavitation effects having asignificant destructive power. This cavitation effect is particularlyimportant at the various interfaces that the acoustic field encounters,for example at the skin, the muscles and the walls of organs. This leadsto poor mastery of tissue destruction, as the latter is not limited tothe zone immediately around the focus of the transducer.

SUMMARY OF THE INVENTION

The present invention thus sets out to resolve the new technicalproblem, which is that of supplying a solution allowing a lesion intissue to be treated which is strictly limited to the focal point of thetreatment device comprising at least one piezoelectric transducerelement, and limiting or avoiding effects due to heat spreading aroundthe focus point, with cavitation phenomena being limited exclusively tothe focal point or to the focal region, and without substantialcavitation phenomena being produced outside said focal point or region.

A further aim of the invention is to resolve the new technical problemby providing a solution which enables a tissue lesion to be treatedwhich is strictly limited to the focal point of the treatment devicecomprising at least one piezoelectric transducer element, at the sametime allowing a point-by-point treatment of the complete tissue area ofthe target requiring treatment to be obtained, such as for examplebenign and malignant tumors well known to those skilled in the art,regardless of whether they be external or internal. Presently preferredapplications are the treatment of benign and malignant tumors of theliver, the prostate, the kidney, the breast, the skin, the brain and thetreatment of varicose effects and of the esophagus.

Yet a further aim of the present invention is to resolve the newtechnical problem consisting in supplying a solution enabling thetemperature of tissue which needs to be protected to be controlled inorder to limit cavitation effects encountered for high acoustic energylevels, such as those required in the performance of therapy, inparticular at the various interfaces and above all at the interfacedefined by the skin of a mammal to be treated, in particular a humanbeing.

All these technical problems are resolved for the first time by thepresent invention in a manner which is simultaneously simple, reliable,inexpensive, and capable of use on an industrial and medical scale.

Thus, according to a first aspect, the present invention provides anapparatus for performing therapy using ultrasound, comprising at leastone treatment device comprising at least one piezoelectric transducerelement designed to provide at least said therapy for the purpose oftreating a target to be treated such as tissue which may be locatedinside the body of a mammal, in particular a human being, and controlmeans for said device in order to carry out said therapy, saidpiezoelectric transducer element being designed to supply ultrasonicwaves focused onto a focal point or region determining the tissue zoneto be submitted to said therapy, characterized in that it comprisescontrol means for said device designed to cause said treatment device tosupply ultrasonic waves of two types, the first type, referred to hereinas thermal waves, producing a predominantly thermal effect on thetissues to be treated, and a second type referred to herein ascavitation waves producing a predominantly cavitation effect on saidtissues to be treated.

In accordance with one advantageous embodiment, the said control meanscontrol within said treatment device, at least at the beginning of saidtreatment, thermal ultrasonic waves.

In accordance with an advantageous embodiment, the said control meansfor the treatment device control the transmission of cavitationultrasonic waves after an adjustable predetermined time intervalallowing pre-heating of the tissue to be treated to be obtained.

In accordance with one special embodiment, the said control means enablethe transmission of cavitation ultrasonic waves to be controlledsimultaneously with the transmission of thermal ultrasonic waves, inparticular after the abovesaid time interval during which only thermalultrasound waves are transmitted.

In accordance with another particular embodiment, the acoustic power ofthe thermal ultrasonic waves is lower than the cavitation thresholdwhereas the acoustic power of the cavitation ultrasonic waves is atleast equal to the cavitation threshold, said cavitation threshold beinga function of the tissue of the mammal to be treated.

In accordance with another embodiment of the invention, the frequency ofsaid cavitation ultrasonic waves is lower than the frequency of saidthermal ultrasonic waves.

In accordance with one embodiment the control means provide fortransmission of cavitation ultrasound waves including a negativecomponent of amplitude of a nature to initiate cavitation.

In accordance with another embodiment the said control means provide thetransmission of cavitation ultrasound waves for a duration comprisedbetween about 0.5 microseconds and about 100 milliseconds, andpreferably comprised between 0.5 microseconds and 50 microseconds.

In accordance with yet another particular embodiment the said controlmeans provide transmission of cavitation ultrasound waves by successivepulses, the repetition frequency of which varies from about 1 Hz to 1KHz, preferably from about 10 Hz to 100 Hz.

In accordance with one particular embodiment the duration of saidadjustable predetermined time interval is comprised between about 100milliseconds and about 10 seconds.

In accordance with yet a further embodiment the total duration oftreatment of the tissue region determined by the focal point or regionby means of the said ultrasound waves is comprised between 100milliseconds and 10 seconds, this total duration including at least onepulse of cavitation ultrasound waves.

In accordance with yet a further particularly advantageous embodiment,the apparatus is characterized in that it comprises means for displacingsaid treatment device in order to perform point-by-point treatment, eachof said points being determined by the said focal point or region, inorder to cover the whole volume of the target to be treated.

Preferably, the said displacement means of the treatment device arecontrolled by a central control unit, comprising for example calculatingmeans such a computer or a micro-computer, the latter being preferablyprovided with software managing the displacement of said treatmentdevice as a function of the volume of the target to be treated, volumedata having advantageously been acquired by imaging means associatedtherewith.

In accordance with yet a further embodiment, the control unit controlsthe displacement of said displacing means of said treatment device inorder to carry out treatment of the tissue regions of the target whichare most remote from said treatment device up to the tissue regions thatare closest to said treatment device in order to improve theeffectiveness of treatment of said target. The invention resolves theproblem of treating remote zones, by treating them first so thatnecrosis of close zones does not stand in the way of treatment of zonesthat are more remote.

In accordance with yet a further advantageous embodiment, the controlmeans provide a latency period between the treatment of two successivepoints on the target to be treated in order to allow said tissue beingtreated to relax, said latency period being preferably comprised betweenabout 1 second and 15 seconds, said latency period being advantageouslyemployed for carrying out the displacement of the treatment device fromone treatment point to another.

In accordance with a further embodiment, the control unit controls adisplacement of said displacement means of said treatment device in arandom manner while nevertheless excluding points that have already beentreated.

In accordance with yet a further embodiment, the frequency oftransmission of said cavitation ultrasound waves is comprised betweenabout 500 KHz and 4 MHz, preferably between 500 KHz and 2 MHz, and evenmore preferably is about 1 MHz.

In accordance with one embodiment, the frequency of transmission of saidthermal ultrasound waves is comprised between about 1 and 4 MHz, saidfrequency being at least equal to the frequency of said cavitationultrasound waves.

In accordance with yet a further embodiment, the acoustic power of saidthermal ultrasound waves is lower than about 150 W/cm², and the acousticpower of said cavitation ultrasound waves is at least equal to about 150W/cm².

In accordance with an advantageous embodiment, the said control meansprovide transmission of ultrasound waves of an amplitude that varies asa function of time, said amplitude preferably increasing with thepassage of time, whereby the amplitude over a first period remains belowa cavitation threshold, then, in a second period becomes higher thansaid cavitation threshold.

From a second independently patentable aspect, the invention providesapparatus for therapy by ultrasound, comprising at least one treatmentdevice designed to provide at least said therapy for the purpose ofdestroying a target to be destroyed such as tissue which may be locatedinside the body of a mammal, in particular a human being, and controlmeans for said device in order to carry out said therapy, saidpiezoelectric transducer element being designed to supply ultrasonichigh energy acoustic waves focused onto a focal point or regiondetermining the tissue zone to be submitted to said therapy, saidultrasound waves passing through tissue regions located at the interfacewith said therapy apparatus, characterized in that it comprises coolingmeans allowing refrigeration or cooling to be performed in apredetermined temperature range, of at least the tissue regions locatedat the interface with said therapy apparatus allowing the tissue regionslocated at said interface to be efficiently protected against cavitationeffects.

In an advantageous embodiment, the cooling means comprise arefrigerating fluid, preferably an aqueous cooling medium such as water.

In a particularly advantageous embodiment, the therapy apparatusincluding said at least one piezoelectric transducer element is providedwith a membrane forming a sealed watertight cavity between said membraneand said piezoelectric transducer element, completely filled withcooling fluid, means for circulating said cooling fluid being alsoprovided in order to ensure renewal and to keep it within the desiredtemperature range.

In one embodiment, the said cooling means also cool said piezoelectrictransducer element.

In another embodiment, a cooling fluid temperature regulating device isprovided, which for example includes one or several temperature sensorswell known in the art.

In accordance with yet a further embodiment, the therapy apparatus isextracorporeal.

In accordance with yet a further embodiment said therapy device is anendo-cavitary device allowing therapy by semi-invasive treatment to beachieved, said endo-cavitary device being in particular an endo-rectalor endo-urethral or even an endo-esophagal device.

In an advantageous embodiment, the temperature of the cooling fluid islower than the mammal's body temperature, and in particular is below 37°C., and even better below 35° C., and better still below 30° C.

A particularly useful range of temperatures is that comprised between 4°C. and 30° C., and even better between 15° C. and 25° C.

In accordance with a particular embodiment, there is included at leastone endo-cavitary device physically independent of said therapy devicefor cooling tissue regions remote from said therapy device and which itis also desired to protect during said therapy. The endocavitary deviceis advantageously fed with the same cooling fluid as the therapyapparatus.

In accordance with yet a further independently patentable embodiment,provision is made for at least one temperature measuring device for thetissue located at the interface with said therapy device, and for meansfor receiving and transmitting temperature data transmitted by thetemperature measuring device to a control unit capable of modifying theinstructions controlling the operation of said therapy apparatus as afunction of the temperature data received. Preferably, the temperaturemeasuring devices comprise sensors in the form of a thermocouple or insheet-form, particularly of the PVDF type which has the advantage ofbeing able to be provided in extremely thin film form, and which canthus be disposed directly on the tissue regions of the interface,opposite the therapy device, or yet again, on the outer side of themembrane enclosing the cooling fluid, said membrane being appliedagainst the surface of the interface tissue. Moreover, here, the sensorwhich is advantageously in sheet form, particularly PVDF-sheet formenables measurement of the ultrasound acoustic pressure field deliveredby the therapy device to be measured at interface level, this making itpossible to know, with considerable accuracy and moreover in real time,what the acoustic power in the focal region is, enabling the electricalpower supplied to the transducer element to be regulated for keeping theultrasonic acoustic field pressure at a constant value at focal point F.

The therapy apparatus can be used with, or applied to, all types oftherapy by ultrasound, preferably focused, of all benign or malignantexternal or internal tumors, and preferably for the treatment of benignand malignant tumors known to those skilled in the art, whether suchtumors be internal or external. Preferred current applications are thetreatment of benign or malignant tumors of the liver, of the prostate,of the kidney, of the breast, of the skin, of the brain and for thetreatment of varicose states and of the esophagus. The invention alsocovers the use or application of such a therapy apparatus formanufacturing equipment for treating benign or malignant tumors.

The invention also covers a therapeutic treatment method which resultsclearly from the preceding description of the apparatus, as well as theembodiments of currently preferred devices which will now be describedin detail with reference to the attached drawings which constitute anintegral part of the invention and in consequence an integral part ofthis present specification.

The invention enables thermal treatment of tissue to be combined withtreatment by cavitation, perfect spatial mastery thereof beingmaintained. The combination of cavitation and thermal treatment has theeffect of reinforcing the destructive potential of treatment, and hencelimiting the duration of treatment pulses and thus avoiding heat energyspreading within the tissue.

In the case of a therapeutic treatment extended to lesions having avolume greater than that of the focal spot, the sequences of treatmentpulses previously described are carried out point-by-point by displacingthe focal point using associated mechanical or electronic control means,between each shot, in order that the focal volume can describe the totalvolume of the lesion.

Similarly, the invention enables a particularly effective cooling of thetissue located in the interface region with the therapy device to beobtained, also ensuring cooling of the piezoelectric transducer elementsof the therapy device, and, in an unexpected manner, the inventionenables the cavitation effects on tissue at the interface region and,also, in the coupling, here constituted by the cooling fluid, to bereduced.

This is moreover achieved in an extremely simple manner since it ispossible to use ordinary tap water, which preferably is degassed, as thelatter is circulating in a closed circuit and is never in contact withthe patient, its temperature being able to be controlled in an extremelysimple manner using all temperature regulation devices well known tothose skilled in the art. Additionally, the water which is present alsohas the advantage of only absorbing very slightly the ultrasound and,consequently, not becoming heated under the action of the ultrasoundfield, thus preserving its cooling capacity.

Another unexpected effect resulting from the limitation of thecavitation effects resides in the fact that it is possible to increasethe power of the acoustic waves and thus to limit the duration oftreatment, which furthermore enables the effects of heating up thetissue, notably by spread of heat, to be limited.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aims, features and advantages of the invention will become moreclear from the description which follows with reference to the attacheddrawings which illustrate three currently preferred embodiments of theinvention, provided simply by way of illustration and which should notbe considered as limiting in any way the scope of the invention. In thefigures:

FIG. 1 is a diagram showing the essential components of an ultrasoundtherapy apparatus according to the present invention;

FIG. 2 shows the threshold of the cavitation effects and the areas ofthermal effects alone, or of thermal effects plus cavitation effects, asa function of acoustic power on the y axis expressed in Watts percentimeter squared, as a function of time on the x axis, expressed inmilliseconds;

FIG. 3 is a diagrammatical representation of the principle ofdestruction of tissue structures by reduction of the cavitationthreshold, with the treatment device shown in FIG. 1, several interfacesbeing identified;

FIG. 4 shows a curve showing how the cavitation threshold varies as afunction of acoustic power along the y axis, expressed in Watts percentimeter squared, versus time on the x axis expressed in milliseconds,the cavitation thresholds for the interfaces in FIG. 3 being indicated;

FIG. 5 shows the thermal ultrasound wave curves and the cavitationultrasound waves as a function of pulse amplitude on the y axis, as afunction of time on the x axis expressed in milliseconds;

FIG. 6 shows another embodiment of the ultrasound waves the amplitude ofwhich increases with the passage of time in order to provide a firstperiod for which this amplitude is less than the cavitation thresholdfollowed by a second period where said amplitude is higher than saidcavitation threshold;

FIG. 7 is a diagrammatic representation showing the frequency ofpoint-by-point treatment, the duration of treatment at each point beingindicated;

FIG. 8 is a block diagram of an extracorporeal therapy apparatusaccording to the present invention including means for cooling tissuesituated at the interface with the therapy device; and

FIG. 9 shows an alternative embodiment of the apparatus in FIG. 8including, additionally, an endo-cavitary cooling probe ensuring tissueregions remote from the therapy device are cooled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, an extracorporeal therapy device according tothe invention is illustrated identified by the general reference number10. This apparatus comprises at least one extracorporeal treatmentdevice bearing the general reference number 12 comprising at least onepiezoelectric transducer element 14 designed to provide at least saidtherapy for the purposes of treating a target to be treated, such astissue, shown diagrammatically by general reference number 16, which maybe situated inside the body of a mammal M, in particular a human being.The skin surface of this mammal is identified by the letter S. Thisapparatus further comprises control means such as 20, 22 controlling thedevice 12, as is shown symbolically by the link 24. The piezoelectrictransducer element 14 is preferably designed to deliver ultrasonic wavesfocused onto a focal point or zone F, the focused acoustic field beingshown symbolically by the letter C. The point of focal zone F obviouslydetermines the tissue region which is to be subjected to said therapy.

The apparatus is characterized in that it comprises control means 20, 22for said treatment device 12 designed to cause said treatment device 12to supply ultrasonic waves of two types, the first type, referred toherein as thermal waves, producing a predominantly thermal effect on thetissues 16 to be treated, and a second type referred to herein ascavitation waves producing a predominantly cavitation effect on saidtissues to be treated.

In an advantageous embodiment, the said control means 20, 22 control,within said treatment device 12, at least at the beginning of saidtreatment, thermal ultrasonic waves.

In another advantageous embodiment, the said control means for thetreatment device control the transmission of cavitation ultrasonic wavesafter an adjustable predetermined time interval allowing pre-heating ofthe tissue to be treated. The said control means advantageously enablethe transmission of cavitation ultrasonic waves to be controlledsimultaneously with the transmission of thermal ultrasonic waves, and inparticular after the abovesaid time interval during which only thermalultrasound waves are delivered.

In another embodiment, the acoustic power of said thermal ultrasonicwaves is lower than the cavitation threshold at focal point F shown indash-dot lines in FIG. 2 and bearing the reference SC, whereas theacoustic power of said cavitation ultrasonic waves is at least equal tothe cavitation threshold SC at focal point F, said cavitation thresholdSC at focal point F being a function of the tissue of the mammal to betreated.

In another embodiment, the frequency of said cavitation ultrasonic wavessent by transducer element 14 under control of control means 20, 22 islower than the frequency of first and second said thermal ultrasonicwaves.

In a further embodiment, said control means provide for transmission ofcavitation ultrasound waves including a negative component of theamplitude thereof of a nature to initiate cavitation.

In a further embodiment, the acoustic power of first and second saidthermal ultrasound waves is lower than about 150 W/cm², and the acousticpower of said cavitation ultrasound waves is at least equal to about 150W/cm². The value of 150 W/cm² as shown in FIG. 2, represents thecavitation threshold at focus point F of the tissue of a cancerous tumorof the body of a mammal, in particular a human being. In FIG. 2, aregion 1 of acoustic power has been shown for which the ultrasound waveshave an acoustic power which extends beyond this cavitation threshold.These ultrasound waves hence exhibit a combination of thermal effectacoustic waves (TEO) and predominantly cavitation-effect ultrasonicwaves (CEO). In contrast, in region 2, the acoustic power of theultrasound waves is well below this cavitation threshold, the ultrasoundwaves being only thermal-effect ultrasonic waves as can be readilyunderstood from FIG. 2.

In one particular embodiment, the frequency of said cavitationultrasonic waves is lower than the frequency of said thermal ultrasonicwaves.

In another embodiment, the control means provide for transmission ofcavitation ultrasound waves including a negative component of theamplitude thereof of a nature to initiate cavitation.

In another embodiment, the said control means 20, 22 provide thetransmission of cavitation ultrasound waves for a duration comprisedbetween about 0.5 microseconds and about 100 milliseconds, andpreferably comprised between 0.5 microseconds and 50 microseconds.

In yet another embodiment, the said control means 20, 22 providetransmission of cavitation ultrasound waves by successive pulses, therepetition frequency of which varies from about 1 Hz to 1 KHz,preferably from about 10 Hz to 100 Hz.

In another embodiment, the duration of said adjustable predeterminedtime interval is comprised between about 100 milliseconds and about 10seconds.

The total duration of treatment, in one embodiment, of the tissue regiondetermined by the focal point or region F by means of the saidultrasound waves is comprised between 100 milliseconds and 10 seconds,this total duration including at least one pulse of cavitationultrasound waves.

In another embodiment, the apparatus is characterized in that itcomprises means 30 for displacing said treatment device 12 in order toperform point-by-point treatment, each of said points being determinedby the said focal point or region F, in order to cover the whole volumeof the target 16 to be treated.

Preferably, the said displacement means 30 of the treatment device 12are controlled by a control means 20, comprising for example calculatingmeans such a computer or a micro-computer, the latter being preferablyprovided with software managing the displacement of said treatmentdevice 12 by suitable control of the displacement means 30 along thethree coordinates X, Y and Z as a function of the volume of the targetto be treated.

Advantageously, an imaging device such as ultrasonographic imagingmeans, bearing the general reference 40 and disposed in a centralopening 42 of treatment device 12 are provided, said imaging device 40being preferably coaxial with focused treatment device 12 so that thefocal point or region F can be monitored permanently. Imaging device 40,as is well known is mounted so as to be advantageously rotatable aboutits common axis identified by arrows R and/or in translation along acommon axis identified by arrow T, through imaging probe displacement 44with a link 46. The imaging device preferably employs a commerciallyavailable ultrasonographic probe using type B ultrasonography, in otherwords sweeping a plane shown in FIG. 1 and bearing reference P. Imagingdevice 40 enables volume data to be obtained on the target 16 to betreated, for transmission to control means 20 for processing by thelatter's software. Control means 20 controls, by unit 30, thedisplacements of treatment device 12 as well as the means 44 fordisplacing the imaging probe 40, in rotation and/or in translation.

In a particular embodiment, the control means 20 controls thedisplacement of said displacing means 30 of said treatment device 12and/or the imaging probe associated therewith, in other words integrallywith the displacement of the treatment device 12, in order to carry outtreatment of the tissue regions of said target which are most remotefrom said treatment device 12, as shown in FIG. 1, up to the tissueregions that are closest to said treatment device 12 in order to improvethe effectiveness of treatment of said target 16.

In accordance with an advantageous embodiment, the control means 20controls a displacement of said displacement means 30 of said treatmentdevice 12 in a random manner while nevertheless excluding points thathave already been treated.

In an advantageous embodiment, the control means 22 provide a latencyperiod between the treatment of two successive points on the target tobe treated in order to allow said tissue being treated to relax, saidlatency period being preferably comprised between about 1 second and 15seconds, said latency period being advantageously employed for carryingout the displacement of the treatment device 12 from one treatment pointto another, by controlling the displacement means 30 from the controlunit. In particular, with reference to FIG. 7, the point-by-pointtreatment sequence has been illustrated. For example, treatment of thefirst point in the first focal region is indicated by F1 and theduration of treatment by t_(F1), the period of latency following this isidentified by t_(L1), whereby the total treatment time from the pointformed by the focal region F1 is t (total for F1). For the followingpoint, point 2, formed by focal region F2, which is different from F1,and which is determined by control unit 20, the treatment time for thispoint F2 is identified by t_(F2), the latency period is identified byt_(L2) and total treatment time is t (total for F2), and so on for theother points.

In accordance with an advantageous further embodiment, the frequency oftransmission of said cavitation ultrasound waves is comprised betweenabout 500 KHz and 4 MHz, preferably between 500 KHz and 2 MHz, and evenmore preferably is about 1 MHz.

In accordance with one embodiment, the frequency of transmission of saidthermal ultrasound waves is comprised between about 2 and 4 MHz, saidfrequency being at least equal to the frequency of said cavitationultrasound waves.

It can thus be seen that the therapy apparatus can be used with, orapplied to, all types of therapy by ultrasound, preferably focused, ofall benign or malignant tumors, whether such tumors be internal orexternal. Preferred current applications are the treatment of benign ormalignant tumors of the liver, of the prostate, of the kidney, of thebreast, of the skin, of the brain and for the treatment of varicosestates and of the esophagus. The invention also covers the use orapplication of such a therapy apparatus as described and illustrated inthe drawings which constitute an integral part of the invention and inconsequence, of the specification, for manufacturing equipment fortreating benign or malignant tumors.

With reference to FIG. 3, the various interfaces (such as the patient'sskin S, internal interfaces of the patient S1 and S2) are indicatedtogether with the focal region F. The treatment device in FIG. 1 bearthe reference 12, the piezoelectric transducer element being identifiedby reference 14, reference 40 indicating the imaging device.

With reference to FIG. 4, the dashed lines show, respectively, theminimum cavitation threshold SC_(min) at 150 W/cm², the cavitationthreshold at interface S, SC_(S), the cavitation threshold at interfaceS1, SC_(S1), and the cavitation threshold at interface S2, SC_(S2), atambient temperature.

Curve SC_(T) shows the curve for the cavitation threshold at the focalpoint as a function of time, and as a function of the temperature of thetissue. Under the effect of temperature increase of the tissue at focalpoint F, the cavitation threshold at focal point SC_(T) diminishes andfalls below the thresholds for cavitation SC_(S) and SC_(min). Windicates the electric control signal supplied by the control means 22to transducer element 14 over time, the amplitude of which enablespredominantly thermal-effect ultrasound waves to be supplied, andelectric signals W1, W2 and W3 of short duration of several microsecondsup to several milliseconds supplied to transducer element 14, allowingthis latter to supply predominantly cavitation-effect ultrasound wavesthe power of which extends beyond the cavitation threshold SC at thefocal point at the instant they are output, as can be seen on FIG. 4.These predominantly cavitation-effect ultrasound waves can besuperimposed on W waves, as shown.

It can be noted that the cavitation waves bearing the references OEC1,OEC2, OEC3 corresponding to the signals W1, W2, W3 are only output aftera predetermined time interval T₁ during which the signals W allow thepredominantly thermal-effect waves to be supplied to perform pre-heatingof the tissue of the focal region F in order to lower the cavitationthreshold at focal point F in a significant manner. This alsoconstitutes one particular preferred technical characteristic, of thepresent invention.

Period T₂ corresponds to the period during which cavitation ultrasoundwaves are output. As already mentioned previously, the frequency oftransmission of cavitation ultrasound waves is comprised between about500 KHz and 4 MHz, preferably between about 500 KHz and 2 MHz, andbetter still about 1 MHz, the transmission frequency of the thermalultrasound waves being about 1 to 4 MHz, this frequency being at leastequal to the frequency of the cavitation ultrasound waves. The duration,moreover, of the cavitation ultrasound waves is comprised between about0.5 microseconds and about 100 milliseconds, and preferably comprisedbetween 0.5 microseconds and 50 microseconds. Moreover, as can be seenin FIG. 7, between the various treatment point F₁, F₂, F₃, F₄, a latencyperiod which is preferably comprised between about 1 second and 15seconds can be seen, said latency period being advantageously employedfor carrying out the displacement of treatment device 12 from one pointto another, as well as for operation of the imaging control means 44 viaa link 46 to imaging means 40.

In FIG. 5, the maximum amplitude A₁ of the predominantly thermal-effectultrasound waves (corresponding to electric signal W) together with themaximum amplitude A₂ of the predominantly cavitation-effect ultrasoundwaves (corresponding to electric signals W₁, W₂, W₃) have been shown.The period of time T₁ during which the cavitation ultrasound waves arenot issued has also been shown, this period advantageously extendingover 100 milliseconds to 10 seconds, the duration of treatment of apoint in the focal region F, t_(F), also being shown together with thetime t₁ which represents the duration of each cavitation ultrasound wavepulse together with the time t₂ between two successive transmissions ofcavitation waves, determining the repetition rate of the cavitationpulses. The end of treatment is eventually accomplished from latencyperiod t_(L).

We have thus determined the total treatment time for point F, which is t(total for F). Thus, referring now to FIG. 7, this data for thetreatment of the first point can be found, bearing subscript 1. Forpoint 4, for example, the relevant data bear the subscript 4, and so on.

Finally, in FIG. 6, another embodiment has been shown in which controlmeans 20, 22 provide transmission of ultrasound waves the amplitude ofwhich varies as a function of time, and preferably where the saidamplitude increases with the passage of time, so that the amplitudeduring a first period T₁ is below a cavitation threshold SC, and thenbecomes higher than the cavitation threshold SC during a second periodT₂.

Referring now to FIG. 8, an independently-patentable alternativeembodiment, which can optionally be combined with the one illustrated inFIGS. 1 to 7 of a therapy apparatus according to the present inventiongenerally identified reference 110 has been shown diagrammatically. Thetissue to be treated is identified by the general reference 112, and theinterface zone which notably comprises the interface tissue that is tobe preserved is identified by general reference 114. The interfacetissue which it is particularly important to preserve is, for example,the skin of a mammal, and preferably of human being.

The therapy apparatus according to the present invention 110 comprisesat least one treatment device 116 comprising at least one piezoelectrictransducer element 118 designed to provide at least said therapy for thepurpose of destroying a target to be destroyed such as tissue 112 whichmay be located inside the body of a mammal M, in particular a humanbeing. The piezoelectric transducer element 118 is designed to supplyfocused ultrasound doses at a focal point or region F determining thetissue region to be subjected to said therapy, the focusing field of theultrasound waves being indicated schematically by reference C.

Control means such as 120, 122 for treatment device 116 for achievingtherapy are also provided. The control means preferably comprise acontrol unit 120, comprising for example calculating means such acomputer or a micro-computer, and mechanical and/or electronic controlmeans 122 for treatment device 116, and hence for the piezoelectrictransducer elements 118, as well known in the art.

In one embodiment, the therapy apparatus 110 is characterized in that itcomprises cooling means 130 allowing cooling to be performed in apredetermined temperature range, of at least the tissue region 114situated at the interface with therapy device 116, providing effectiveprotection of the tissue zones at said interface 114.

Advantageously, the cooling means 130 comprise a refrigerating fluid,132, preferably a liquid refrigerating medium such as in particular,degassed water.

According to a further particularly advantageous embodiment, therapydevice 116 is provided with a membrane in the form of a pocket or bag,fixed in a sealed manner onto treatment device 116, as will be readilyunderstood by those skilled in the art from FIG. 8. This membrane, whichis closed in a sealed manner, is completely filled with cooling liquid132. Means 136 for circulating the cooling liquid are also provided forthe purposes of renewing it, and for keeping it in the intended coolingtemperature region. According to one special embodiment, the coolingmeans 130 also provide cooling of the piezoelectric transducer element118, which is generally the case when membrane 134 externally surroundsat least the transducer element 118 so that the latter is immersed or isin permanent contact with cooling liquid 132.

The circulating means 136 comprise, for example, a conduit 138 forintroducing cooling fluid from a constant temperature device 140 whichincludes at least one temperature regulation device 142 which controls acooling unit 144, for example a heat exchanger, device 142 being coupledto one or several temperature sensors 146, 148 one of which, such as theone bearing the reference 146, being able to be disposed in the coolingliquid 132 and the other one, such as 148, being arranged externally tomembrane 144, between the latter and the surface S of the skin of themammal M. The cooling fluid leaves through a conduit 139 in order toreturn to cooling unit 144, optionally passing through a degassingdevice 150. Circulation pumps such as the one indicated by reference 152can obviously be provided.

The complete cooling means are advantageously controlled by control unit120.

Moreover, a pressure sensing device 154 also inserted externally betweenthe membrane 134 and surface S of the skin of mammal M can also beprovided, for transmitting pressure data over a corresponding conductorelement 156 to control unit 120 so that the latter can modify thecommands sent out to the control means 122.

According to the a particularly advantageous embodiment of the inventionshown in FIG. 8, the therapy device 110 is extra-corporeal.

According to another embodiment, which is not shown, the therapy devicecan be an endocavitary device allowing semi-invasive therapy to beperformed; this endocavitary device can in particular be anendo-urethral or an endo-rectal device. It can also be an endo-esophagaldevice. As the provision of such an endocavitary device is well known tothose skilled in the art, it was considered not to be necessary to showthis in the figures. Reference can also be made to U.S. Pat. Nos.5,316,000 and 5,474,071.

The tissue temperature measuring devices such as 148 advantageouslycomprise sensors in thermocouple form, or in sheet form, particularly ofthe PVDF type which has the advantage of being able to be provided inextremely thin film form, and which can thus be disposed directly on thetissue regions of the interface, opposite the therapy device 116, or yetagain, on the outer side of membrane 134 as shown, said membrane beingapplied against the surface S of interface tissue 114. Moreover, here,the sensor 154 which is advantageously in sheet form, particularlyPVDF-sheet form enables measurement of the ultrasound acoustic pressurefield delivered by therapy device 116 to be measured at interface 114level, this making it possible to know, with considerable accuracy andmoreover in real time, what the acoustic power in the focal region is.

Referring now to FIG. 9, an alternative embodiment of the apparatus inFIG. 8 has been shown, at least one endocavitary device 160 which isphysically independent of therapy device 116 being provided, for thecooling of tissue regions that are remote from therapy device 116 andwhich it is also desired to protect during therapy. The saidendocavitary device 160 is advantageously designed to receive the samecooling fluid 132 as the one use for therapy device 116. Here fortreatment of the prostate P, the urethra U is shown diagrammatically,and endocavitary device 160 is an endo-urethral device. Endocavitarydevice 160 comprises a conduit 138A for supplying cooling fluid 132which branches off conduit 138 in FIG. 8, and an evacuation conduit 139Abranching off outlet conduit 139 in FIG. 8, this only representing anextremely minor modification of the overall apparatus.

It can also be arranged for the endocavitary probe 160 to be fitted withtemperature measuring devices allowing the temperature urethra U hasreached to be checked, thus introducing additional safely intotreatment.

How the apparatus shown in FIGS. 8 and 9 operates will be immediatelyapparent to those skilled in the art, from the description above.

It should be pointed out, while on this matter, that it is preferred touse for the focused piezo-electric transducer element, a transducerelement with an opening 1 and which operates at a frequency of 1 MHz.For this type of transducer element, the volume of focal region F willtypically be of elliptical shape, as illustrated, the major axis being10 mm long and the minor axis 2 mm.

Here, it will be noticed that the volume of focal region F is very smallcompared to the size of prostate P, the latter defining the total volumeof the tissue region that is to be treated by ultrasound therapy.

Bearing in mind that the volume of focal region F is very small comparedto the total volume of the tissue to be treated, it suffices to displacetreatment device 116 during treatment in order to achieve so-calledpoint-by-point treatment covering the whole of the volume of the lesionto be treated.

It will be understood that in the case of particularly intense heatbeing created within focal volume F, heat energy spreads through tissuethat may extend well beyond that of the lesion to be destroyed,invading, in particular, the tissue region that is to be preserved suchas tissue region 114. This particularly applies when the focal volume Fis quite close to the tissue region to be preserved, such as region 114in FIGS. 8 to 9.

Such protection is also ensured by cooling at least tissue region 114(FIG. 8), and optionally the region U of the urethra in FIG. 9., thanksto the presence of membrane 134 situated in contact with the tissue 114,and, optionally, thanks to the presence of the supplementaryendocavitary probe 160.

Membrane 134 is characterized by its transparency to the acoustic field,and its thermal conducting capacity. A suitable material is chosen toprovide said characteristics, such as latex or silicone rubber. Membranethickness in the region where the acoustic field passes is preferablyreduced to a minimum. It can vary from several micrometers up to severalmillimeters, depending on the application envisaged (extracorporeal orendocavitary).

Thanks to the control provided by control unit 120 and temperatureregulating device 140, cooling fluid 132 is cooled down to apredetermined temperature that is lower than the mammal's bodytemperature, and in particular is below 37° C., and even better below35° C., and better still below 30° C. A particularly useful range oftemperatures is that comprised between 4° C. and 30° C., and even betterbetween 15° C. and 25° C.

It should be noted that in FIG. 8 the temperature and/or pressuresensors 148, 154 in the form of extremely thin sheet(s) are transparentto the acoustic field and do not in practice cause any interference.Given that these sensors are sensitive to pressure, they enable theacoustic field pressure'supplied by focused transducer element 118 to bemeasured. The pressure information is transmitted to the control unit120 for commanding the control means 122, notably for varying theelectrical power fed to the ultrasound acoustic transducer element.

It is obviously possible to apply an acoustic coupling compound, such assilicone grease, to the patient's skin when carrying out therapy.

A positioning device, such as device 40 in FIG. 1 can also be providedfor accurately positioning the focal region F of focused transducerelement 118 of FIG. 8 opposite the lesion to be destroyed.

The choice of how much ultrasound power to use depends on the depth ofthe lesion to be destroyed. Ultrasound power is controlled and regulatedduring successive shots by pressure sensing device 154.

In FIG. 8, as soon as shooting starts, temperature sensor 148 measuresthe temperature reached by the tissue that is to be preserved 114,which, in this case, is the patient's skin, for supply of the relevantinformation to temperature regulating device 136. The latter device actson cooling unit 144 in order to keep the temperature of tissue to bepreserved at a constant determined value, in order to avoid or limitcavitation effects resulting from the therapeutic high energy ultrasoundacoustic waves employed. Regulation is achieved by reducing to a greateror smaller extent the temperature of cooling fluid 132, which preferablyis a liquid such as degassed tap water.

It can thus be seen that the invention enables the determining technicaladvantages stated above to be achieved in a simple, safe and effectivemanner from the therapeutic point of view, and with considerableversatility ensuring ready adaptability to all types of lesions to betreated. The invention obviously covers all means that are technicalequivalents of the means described as well as various combinationsthereof.

Moreover, the invention covers all technical means that appear to benovel over any state of the art and which result from the precedingdescription in combination with the drawings which constitute anintegral part thereof.

What is claimed is:
 1. A therapy method using ultrasound for the purposeof destroying a target to be destroyed, said target including tissuewhich may be located inside a body of a mammal, by supplying ultrasonicwaves focused onto a focal point or region F determining a tissue zoneto be submitted to said therapy, which comprises supplying ultrasonicwaves of two types, thermal waves, for producing a predominantly thermaleffect on tissue to be treated, and cavitation waves, for producing apredominantly cavitation effect on said tissue to be treated, said twotypes of waves being applied for a time sufficient to effect therapy bydestroying at least a portion of said tissue.
 2. A therapy method usingultrasound for the purpose of destroying a target to be destroyed, saidtarget including tissue which may be located inside a body of a mammal,by supplying ultrasonic waves focused onto a focal point or region Fdetermining a tissue zone to be submitted to said therapy, whichcomprises supplying ultrasonic waves of two types, thermal waves, forproducing a predominantly thermal effect on tissue to be treated, andcavitation waves, for producing a predominantly cavitation effect onsaid tissue to be treated, said two types of waves being applied for atime sufficient to effect therapy by destroying at least a portion ofsaid tissue and wherein said thermal ultrasonic waves are supplied atleast at a beginning of treatment.
 3. The method according to claim 2,wherein said cavitation ultrasonic waves are supplied after anadjustable predetermined time interval for allowing preheating of thetissue to be treated.
 4. The method according to claim 3, wherein saidcavitation ultrasonic waves are supplied simultaneously with saidthermal ultrasonic waves.
 5. The method according to claim 3, whereinacoustic power of said thermal ultrasonic waves is lower than acavitation threshold whereas acoustic power of said cavitationultrasonic waves is at least equal to the cavitation threshold, saidcavitation threshold being a function of the tissue of the mammal to betreated.
 6. The method according to claim 3, wherein the frequency ofsaid cavitation ultrasonic waves is lower than the frequency of saidthermal ultrasonic waves.
 7. The method according to claim 3, whereinsaid cavitation ultrasound waves include a negative amplitude componentof a nature to initiate cavitation.
 8. The method according to claim 3,wherein said cavitation ultrasound waves are supplied for a duration ofbetween about 0.5 microseconds and about 100 milliseconds.
 9. The methodaccording to claim 3, wherein said cavitation ultrasound waves aresupplied by successive pulses, repetition frequency of which varies fromabout 1 Hz to about 1 KHz.
 10. The method according to claim 3, whereinthe duration of said adjustable predetermined time interval is betweenabout 100 milliseconds and about 10 seconds.
 11. The method according toclaim 3, wherein the total duration of treatment of the tissue regiondetermined by the focal point or region F by means of the saidultrasound waves is between about 100 milliseconds and 10 seconds, thistotal duration including at least one pulse of cavitation ultrasoundwaves.
 12. The method according to claim 3, wherein the frequency oftransmission of said cavitation ultrasound waves is between about 500KHz and about 4 MHz.
 13. The method according to claim 3, wherein thefrequency of transmission of said thermal ultrasound waves is betweenabout I 1 and about 4 MHz, said frequency being at least equal to thefrequency being at least equal to the frequency of said cavitationultrasound waves.
 14. The method according to claim 3, wherein theacoustic power of said thermal ultrasound waves is lower than about 150W/cm², and the acoustic power of said cavitation ultrasound waves is atleast equal to about 150 W/cm².
 15. The method according to claim 3,further comprising the step of providing transmission of ultrasoundwaves of an amplitude that varies as a function of time, said amplitudepreferably increasing with the passage of time, whereby the amplitudeover a first period remains below a cavitation threshold, then, in asecond period becomes higher than said cavitation threshold.
 16. Themethod according to claim 30, further comprising the step of displacingsaid focal point to perform point-by-point treatment, each of saidpoints being determined by the said focal point or region F, in order tocover the entire volume of the tissue target to be treated.
 17. Atherapy method using ultrasound for the purpose of destroying a targetto be destroyed, said target including tissue which may be locatedinside a body of a mammal, by supplying ultrasonic waves focused onto afocal point or region F determining a tissue zone to be submitted tosaid therapy, which comprises supplying ultrasonic waves of two types,thermal waves, for producing a predominantly thermal effect on tissue tobe treated, and cavitation waves, for producing a predominantlycavitation effect on said tissue to be treated, said two types of wavesbeing applied for a time sufficient to effect therapy by destroying atleast a portion of said tissue, displacing said focal point to performpoint-by-point treatment, each of said points being determined by thesaid focal point or region F, in order to cover the entire volume of thetissue target to be treated, and conducting an imaging step to acquirevolume data so that said focal point may be displaced as a function ofthe volume of the target to be treated.
 18. The method according toclaim 17, further comprising the step of displacing the focal point inorder to carry out treatment of the tissue regions of said target whichare most remote from said ultrasonic waves up to the tissue regions thatare closest to said ultrasonic waves so as to improve effectiveness oftreatment of said target.
 19. The method according to claim 17, furthercomprising the step of displacing the focal point with a latency periodbetween treatment of two successive points on the target to be treatedin order to allow said tissue being treated to relax, said latencyperiod being between about 1 second and 15 seconds and being employedfor carrying out displacement of the focal point from one treatmentpoint to another.
 20. The method according to claim 17, furthercomprising the step of displacing the focal point in a random mannerwhile excluding points that have already been treated.
 21. An apparatusfor performing therapy using ultrasound, comprising at least onetreatment device comprising at least one piezoelectric transducerelement designed to provide at least said therapy for the purpose ofdestroying a target to be destroyed, said target including tissue whichmay be located inside a body of a mammal, and control means for saiddevice in order to carry out said therapy, said piezoelectric transducerelement being designed to supply ultrasonic waves focused onto a focalpoint or region F determining the tissue zone to be submitted to saidtherapy, said apparatus further comprising control means for causingsaid treatment device to supply ultrasonic waves of two types, thermalwaves, for producing a predominantly thermal effect on the tissues to betreated, and cavitation waves, for producing a predominantly cavitationeffect on said tissues to be treated when such tissues are exposed tosaid two types of ultrasonic waves.
 22. An apparatus for performingtherapy using ultrasound, comprising at least one treatment devicecomprising at least one piezoelectric transducer element designed toprovide at least said therapy for the purpose of destroying a target tobe destroyed, said target including tissue which may be located inside abody of a mammal, and control means for said device in order to carryout said therapy, said piezoelectric transducer element being designedto supply ultrasonic waves focused onto a focal point or region Fdetermining the tissue zone to be submitted to said therapy, saidapparatus further comprising control means for causing said treatmentdevice to supply ultrasonic waves of two types, thermal waves, forproducing a predominantly thermal effect on the tissues to be treated,and cavitation waves, for producing a predominantly cavitation effect onsaid tissues to be treated when such tissues are exposed to said twotypes of ultrasonic waves, wherein said control means causes saidtreatment device to transmit thermal ultrasonic waves at least at thebeginning of said treatment.
 23. The apparatus according to claim 22,wherein said control means cause said treatment device to transmitcavitation ultrasonic waves after an adjustable predetermined timeinterval allowing pre-heating of the tissue to be treated.
 24. Theapparatus according to claim 23, wherein said control means causes thetransmission of cavitation ultrasonic waves simultaneously with thetransmission of thermal ultrasonic waves.
 25. The apparatus according toclaim 23, wherein acoustic power of said thermal ultrasonic waves islower than a cavitation threshold whereas acoustic power of saidcavitation ultrasonic waves is at least equal to the cavitationthreshold, said cavitation threshold being a function of the tissue ofthe mammal to be treated.
 26. The apparatus according to claim 23,wherein a frequency of said cavitation ultrasonic waves is lower than afrequency of said thermal ultrasonic waves.
 27. The apparatus accordingto claim 23, wherein said control means causes transmission ofcavitation ultrasound waves including a negative component of theamplitude thereof of a nature to initiate cavitation.
 28. The apparatusaccording to claim 23, wherein said control means causes transmission ofcavitation ultrasound waves for a duration of between about 0.5microseconds and about 100 milliseconds.
 29. The apparatus according toclaim 23, wherein said control means provides transmission of cavitationultrasound waves by successive pulses, the repetition frequency of whichvaries from about 1 Hz to about 1 KHz.
 30. The apparatus according toclaim 23, wherein the duration of said adjustable predetermined timeinterval is between about 100 milliseconds and about 10 seconds.
 31. Theapparatus according to claim 23, wherein the total duration of treatmentof the tissue region determined by the focal point or region F by meansof the said ultrasound waves is between 100 milliseconds and 10 seconds,this total duration including at least one pulse of cavitationultrasound waves.
 32. The apparatus according to claim 23, whereinfrequency of transmission of said cavitation ultrasound waves is betweenabout 500 KHz and about 4 MHz.
 33. The apparatus according to claim 23,wherein frequency of transmission of said thermal ultrasound waves isbetween about 1 and about 4 MHz, said frequency being at least equal tothe frequency of said cavitation ultrasound waves.
 34. The apparatusaccording to claim 23, wherein acoustic power of said thermal ultrasoundwaves is lower than 150 W/cm², and the acoustic power of said cavitationultrasound waves is at least equal to about 150 W/cm².
 35. The apparatusaccording to claim 23, wherein said control means provides transmissionof ultrasound waves of an amplitude that varies as a function of time,said amplitude preferably increasing with the passage of time, wherebythe amplitude over a first period remains below a cavitation threshold,then, in a second period becomes higher than said cavitation threshold.36. The apparatus according to claim 22, comprising means for displacingsaid treatment device in order to perform point-by-point treatment, eachof said points being determined by the said focal point or region F, inorder to cover the entire volume of the target to be treated.
 37. Anapparatus for performing therapy using ultrasound, comprising at leastone treatment device comprising at least one piezoelectric transducerelement designed to provide at least said therapy for the purpose ofdestroying a target to be destroyed, said target including tissue whichmay be located inside a body of a mammal, and control means for saiddevice in order to carry out said therapy, said piezoelectric transducerelement being designed to supply ultrasonic waves focused onto a focalpoint or region F determining the tissue zone to be submitted to saidtherapy, said apparatus further comprising control means for causingsaid treatment device to supply ultrasonic waves of two types, thermalwaves, for producing a predominantly thermal effect on the tissues to betreated, and cavitation waves, for producing a predominantly cavitationeffect on said tissues to be treated when such tissues are exposed tosaid two types of ultrasonic waves and means for displacing saidtreatment device in order to perform point-by-point treatment, each ofsaid points being determined by the said focal point or region F, inorder to cover the entire volume of the target to be treated, whereinsaid displacement means of the treatment device are controlled by acontrol unit which includes a computer or micro-computer, the latterbeing provided with software managing displacement of said treatmentdevice as a function of the volume of the target to be treated, volumedata having advantageously been acquired by imaging means associatedtherewith having special imaging control means controlled by saidcontrol unit for translatory or rotational displacement.
 38. Theapparatus according to claim 37, wherein said control unit controls thedisplacement of said displacement means of said treatment device inorder to carry out treatment of the tissue regions of said target whichare most remote from said treatment device up to the tissue regions thatare closest to said treatment device in order to improve theeffectiveness of treatment of said target.
 39. The apparatus accordingto claim 37, wherein said control means provides a latency periodbetween treatment of two successive points on the target to be treatedin order to allow said tissue being treated to relax, said latencyperiod being between about 1 second and 15 seconds, said latency periodbeing employed for carrying out displacement of the treatment devicefrom one treatment point to another.
 40. The apparatus according toclaim 37, wherein said control unit controls displacement of saiddisplacement means of said treatment device in a random manner whileexcluding points that have already been treated.